Purification and characterization of two agarases from Agarivorans albus OAY02

Two extracellular beta-agarases were purified from Agarivorans albus OAY2, which was isolated from seaweed collected in Qingdao, Shandong, China. The fermentation process was optimized with enzyme activity improving from 1.06 U/ml to 2.65 U/ml. Agarases were purified by ammonium sulfate fractionation and ion-exchange chromatography. Purification resulted in a 107-fold increase in agarase-a activity and a 52-fold increase in case of agarase-b, with high specific activities of 2715 and 1338 U/mg, respectively. The molecular masses of the agarases were estimated to be 50 kDa and 107 kDa, respectively. The optimum temperatures for the activities of agarase-a and agarase-b were 40 degrees C and 50 degrees C, respectively. Agarase-a was stable at 30 C, while agarase-b was stable at 50 degrees C. The optimum pH values for agarase-a and agarase-b were both 9.0. Agarase-a was inhibited by Cu2+, Mn2+, Co2+ and EDTA, while agarase-b was inhibited by Cu2+, Mn2+ and Fe2+. The results of C-13 NMR and TLC showed that hydrolysis of agarose by agarase-a produced neoagarobiose (NA2), neoagarotetraose (NA4) and neoagarohexaose (NA6). Agarase-b hydrolyzed agarose to yield neoagarobiose (NA2) and neoagarotetraose (NA4). Evaluation of matrix-assisted laser desorption ionization/time-of-flight MS (MALDI-TOF-TOF/MS) and the enzymatic product results indicated that agarase-a and agarase-b might be novel agarases. (C) 2014 Elsevier Ltd. All rights reserved.